Output torque control apparatus and method for an internal combustion engine

ABSTRACT

The invention provides an output torque control method and apparatus for a lean burn internal combustion engine which accounts for aging of component parts, and in which no stepwise change of torque or shock occur when an air fuel ratio is changed. The method and apparatus according to the invention control an intake air amount while maintaining an emission purification function by controlling the air fuel ratio to that of a theoretical mixture (air fuel ratio of 14.7) in a case where a limit NOx emission is determined by using a detected air fuel ratio and lean burn operation becomes difficult due to the amount of NOx emissions. Abrupt change of an output torque when the air fuel ratio is changed is curtailed by controlling a fuel amount or an air amount after calculating the fuel amount or the air amount from an engine speed and an accelerator depression angle.

This is a continuation of application Ser. No. 08/788,565, filed Jan.24, 1997, now U.S. Pat. No. 5,752,485 which is a continuation ofapplication Ser. No. 08/491,245, filed Jun. 16, 1995, now U.S. Pat. No.5,660,157.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for controllingthe output torque of an automotive internal combustion engine,especially a lean burn internal combustion engine.

BACKGROUND OF THE INVENTION

A lean burn internal combustion engine is an internal combustion enginein which an air fuel ratio--the ratio of the quantity of intake air(intake amount) to the quantity of fuel--is larger than a theoretical(stoichiometric) air fuel ratio; that is, it is operated at a lean airfuel ratio wherein the intake amount is larger than the fuel amount. Incontrolling a conventional lean burn internal combustion engine, forexample, as described in Japanese Unexamined Patent Publication No.34329/1976, a method has been proposed in which fuel consumption isimproved by controlling the air fuel ratio in accordance with periodicvariation of average pressure in a combustion chamber, and increasing anoperating region of lean burn.

Further, Japanese Unexamined Patent Publication No. 160530/1983,discloses a method in which exhaust gas recirculation, ignition timingand air fuel ratio are controlled in accordance with a variation intorque, which is calculated by combustion pressure and the like.

However, in increasing the operating region of lean burn to improve fuelcost, the objective of reducing a poisonous component of exhaust gas(emission of a nitrogen oxide component, hereinafter referred to asNOx), is not considered; and therefore, the control of a lean burninternal combustion engine is incomplete. Further, the reduction ofpoisonous components in exhaust gas and the operational performancedeteriorate over time in comparison with their initial states, due toaging of component parts of the lean burn internal combustion engine andcomponent parts of a control device.

In addition, the lean burn air fuel ratio is switched to the theoreticalair fuel ratio when large power output is required since the output isinsufficient in the lean burn state in comparison with the combustionstate at the theoretical air fuel ratio. However, in switching the airfuel ratio, the fuel amount is changed while the intake amount remainsconstant, and therefore the output torque is abruptly changed, adverselyaffecting handling of the vehicle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andapparatus for controlling output torque of a lean burn internalcombustion engine which takes into account the above-mentioned aging,does not increase the fuel cost, furthers the objective of reducingpoisonous components of exhaust gas, and improves the operationalperformance, without causing an abrupt change of torque, even when theair fuel ratio is changed.

To achieve the above object, the present invention includes a target airfuel ratio data calculating unit which calculates target air fuel ratiodata for a lean burn internal combustion engine based on the intakeamount, the depression angle of an accelerator pedal and rotationalvelocity of the engine; a torque detecting device for detecting anoutput torque showing an operational state of the engine; a lean burnlimit determining unit for determining a limit region of lean burn inaccordance with change of the output torque; air fuel ratio detectingdevice for detecting the air fuel ratio; a NOx emission amount/limit airfuel ratio determining unit for determining a limit air fuel ratiocorresponding to a predetermined limit for NOx emissions by using theair fuel ratio; an air fuel ratio correcting unit for outputting acorrected air fuel ratio value corresponding to a lean burn limit whichhas been determined by the above-mentioned lean burn limit determiningunit; a target air fuel ratio data changing device for rewriting andchanging a target air fuel ratio data in accordance with the correctedair fuel ratio from the air fuel ratio correcting unit and the correctedair fuel ratio from the NOx emissions amount limit air fuel ratiodetermining unit; a target air fuel ratio data storage unit for storingthe target air fuel ratio data used for calculating the fuel amount; afuel amount calculating unit for calculating the fuel amount using thetarget air fuel ratio data and the corrected air fuel ratio; and a fuelinjection valve for supplying the lean burn internal combustion enginewith the fuel amount which has been calculated by the fuel amountcalculating means.

By means of the above-mentioned construction, a NOx emission limit isdetermined based on the air fuel ratio obtained from the air fuel ratiodetecting unit, and the air fuel ratio is adjusted to the theoreticalmixture (air fuel ratio=14.7) when the lean burn operation becomesdifficult in view of the NOx emission amount, to thereby maintain theemission control function. Further, the output torque of the internalcombustion engine can be prevented from changing by adding a torquecorrection which controls the air intake so as to adapt to the air fuelratio control. In this arrangement, improvement of fuel cost by the leanburn limit control and maintaining the emission control functionby-determining the limit NOx emission limit are compatible with eachother.

Another embodiment of the present invention includes a steady state(normal) fuel amount calculating device for calculating the fuel amountbased on the engine speed and an accelerator depression angle with theengine operated at lean burn or at the theoretical air fuel ratio; and adevice for calculating an adjusted fuel amount to avoid abrupt(stepwise) torque change or shock when the air fuel ratio is switched,based on the engine speed and the accelerator depression angle, when thestate of the engine is switched from either one of the above twocombustion states to the other combustion state.

Further, still another embodiment of the present invention includes thesteady state intake amount calculating unit for calculating the intakeamount based on the engine speed and the accelerator depression anglewith the engine operated at lean burn or at the theoretical air fuelratio; and a device for calculating an adjusted air amount to avoidabrupt torque change when the air fuel ratio is switched, based on theengine speed and the accelerator depression angle when the engine isswitched from either one of the above two combustion states to the othercombustion state.

With the above construction, the engine is controlled such that the fuelamount or the intake amount is changed in switching the air fuel ratioso that an abrupt torque change, and therefore, advance vehicle handlingeffects caused by such an abrupt change, can be alleviated.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of an automobile power train system;

FIG. 2 is block diagram showing the manner of controlling an outputtorque of an engine;

FIG. 3 is a block diagram showing a specific embodiment for controllingan output torque of an engine;

FIG. 4 is a flow chart which shows the process performed by the controlin FIG. 3;

FIG. 5 is a flow chart which shows the process performed by the controlin FIG. 3;

FIG. 6 is a flow chart which shows the process performed by the controlin FIG. 3;

FIG. 7 depicts an operating characteristic which represents therelationship between an air fuel ratio and a NOx emission amount;

FIG. 8 is a block diagram showing a control arrangement which includescontrol of the air amount;

FIG. 9 is a flow chart which shows the process performed by the controlin FIG. 8;

FIG. 10 is a conceptual view of a control arrangement which shows mapsof basic control of a lean burn internal combustion engine;

FIG. 11 is a block diagram showing a control arrangement which includescontrol of ignition timing;

FIG. 12 is a flow chart which shows the process performed by the controlin FIG. 11;

FIG. 13 is another flow chart which shows the process performed by thecontrol in FIG. 11;

FIG. 14 is a block diagram of a control arrangement for preventing shockcaused by a change in an air fuel ratio;

FIG. 15 illustrates time charts for explaining the control of FIG. 14;

FIG. 16 is a block diagram of a control in another embodiment;

FIG. 17 is a graph showing the relationship between air fuel ratio andfuel amount;

FIG. 18 is a graph showing the relationship between air fuel ratio andNOx emissions;

FIG. 19 is a time chart showing the change of output torque of anengine;

FIG. 20 is a time chart showing another change of output torque of anengine;

FIG. 21 is a flow chart which shows the calculation performed by an airfuel ratio switch time fuel injection amount calculating means;

FIG. 22 is a flow chart which shows the calculation performed by asteady state time fuel injection amount calculating means;

FIG. 23 is a flow chart which shows the calculation performed by an airfuel ratio switch throttle opening degree calculating means;

FIG. 24 is a flow chart which shows the calculation performed by anormal state time throttle opening degree calculating means;

FIG. 25 is a flow chart which shows the calculation performed by an airfuel ratio switch time detecting means;

FIG. 26 is a flow chart which shows the calculation performed by a fuelinjection amount calculation value selecting means; and

FIG. 27 is a flow chart which shows the calculation performed by athrottle opening degree calculation value selecting means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention is shown in FIGS. 1 through7. FIG. 1 is a schematic view of an automotive drive train. Attached toan engine 1 are a change gear 2, an intake pipe 3, an exhaust pipe 4,fuel injection valves 5 and ignition plugs 6. Intake air flowing intothe engine after passing through the intake pipe 3 and fuel injectedfrom the fuel injection valves 5 are mixed into a mixture which isignited and combusted by the ignition plugs 6 and a change of pressurein the combustion is converted into an output in the form of arotational motion. The change gear 2 reduces the speed of the rotationalmotion and transmits it to a drive shaft 7 of an automobile. Therotational motion of the drive shaft 7 is transmitted to wheels 9 via adifferential gear 8 whereby the automobile can run on roads. The engine1 and the change gear 2 are electrically connected to a control unit 10and signals are sent and received therebetween. Input signals to thecontrol unit 10 are sent from an accelerator depression angle sensor 11,an air flow (intake amount) sensor 12, an input shaft rotation sensor 13attached to an input shaft of a torque converter in the change gear 2for measuring an engine speed, an output shaft rotation sensor 14attached to an output shaft of the torque converter, an output shaftrotation sensor 15 attached to an output shaft of the change gear 2connected to the driver shaft 7, a torque sensor 16 and an oxygen sensor17 attached to the exhaust pipe 4. Output signals are sent from thecontrol unit 10 to a throttle control device 18 for adjusting intake airamount in the intake pipe 3, a drive motor 20 for driving swirl shuntvalves 19 each generating a swirl flow in the intake air to acceleratecombustion, the fuel injection valves 5, the ignition plugs 6 and aspeed change controlling actuator 21 each of which is controlled by eachof the output signals. The oxygen sensor 17 can determine the air fuelratio by measuring oxygen concentration in the exhaust gas andtherefore, it can be used as an air fuel ratio sensor. Further, a threeway catalyst 22 and a NOx reduction catalyst 23 are installed to theexhaust gas 4 to purify the exhaust gas.

FIG. 2 is a block diagram showing an arrangement for controlling anoutput torque of the engine 1 according to the invention. A target airfuel ratio data calculating unit 204 calculates a target air fuel ratiofrom data sent from an engine speed sensor 201, an intake air amountsensor 202 and an accelerator depression angle sensor 203, and sends itto a target air fuel ratio data storing unit 205. Meanwhile, a torquedetecting unit 206 detects a torque value indicative of the operationalstate of the engine 1; a lean burn limit determining unit 207 determinesa limit of lean burn while detecting a change of the torque; an air fuelratio correcting unit 208 calculates a corrected value of the air fuelratio corresponding to the determined limit of lean burn and sends it toa target air fuel ratio data changing unit 209. Further, a NOx emissionamount limit air fuel ratio determining means 211 determines a limit airfuel ratio having lower NOx emissions based on the air fuel ratiodetected by an air fuel ratio detecting unit 210, and sends thecorrected value of the air fuel ratio corresponding thereto to thetarget air fuel ratio data changing unit 209. The target air fuel ratiodata changing unit 209 rewrites and changes the target air fuel ratiodata stored in the target air fuel ratio data storing unit 205 inaccordance with the corrected value of the air fuel ratio from the airfuel ratio correcting unit 208 and the limit air fuel ratio determiningunit 211. Next, the rewritten target air fuel ratio data is againcorrected by the correction value from the air fuel ratio correctingunit 208 and sent to a fuel amount calculating means 212. The fuelamount calculating means 212 calculates a fuel amount based on the senttarget air fuel ratio data, and sends the data of the fuel amount to afuel injection device 213 whereby the fuel amount in accordance with thevalue of the calculated target air fuel ratio data is supplied to theengine 1. In this way, the actual lean burn limit air fuel ratio iscompared with the NOx emission limit air fuel ratio and the target airfuel ratio is set based on the determination. Therefore, it is possibleto attain air fuel ratio control capable of coping with aging ofmechanical devices or the like and the fuel cost reduction and theexhaust gas purification can be compatible with each other.

FIG. 3 is a block diagram showing a specific arrangement for controllingan output torque of an engine. Existing sensors are used here in view oftheir cost and mounting performance. Torque variation in the vicinity ofa lean burn limit is detected by calculating a surge index based on therate of change of the engine speed in block 301 and determining the leanburn limit in block 302. Next, a corrected air fuel ratio is calculatedin block 303, based on the lean burn limit determined in block 302.Concurrently, the operation detects the oxygen amount very accurately,using the oxygen sensor 17 by which the air fuel ratio is predicted.That is, in block 306 the operation determines the target air fuel ratiodata when the target air fuel ratio becomes the theoretical air fuelratio (air/fuel=14.7) and corrects the air fuel ratio in lean burn bythe result of learning the theoretical air fuel ratio. In block 307, theoperation reads the target air fuel ratio data from the target air fuelratio data storing means 205 shown in FIG. 2, calculates the fuel amountand outputs the data to the fuel injection valve 5 in block 308. In thiscase, the operation adds the corrected air fuel ratio calculated inblock 303 to the target air fuel ratio read in block 307 to therebycorrect the target air fuel ratio. Also, the operation determineswhether or not the target air fuel ratio data read in block 307 is equalto the NOx emission limit air fuel ratio in block 305. If it is, inblock 304 the operation changes the target air fuel ratio data read inblock 307 by the corrected air fuel ratio sent from block 303.

FIGS. 4 through 6 are flow charts which illustrate the operation of thecontrol arrangement shown in FIG. 3. FIG. 4 shows the operation ofblocks 301 through 304 in FIG. 3. Firstly, in step 401 the operationreads signals Nem and Nec from two systems of pulse width measuring andpulse number counting, to accurately detect the engine speed. Next, instep 402, the operation determines whether the engine is presentlyoperating in a steady state, by comparing consecutive engine speedmeasurements. Xm(n-1) and Xm(n-2) respectively designate the pulse widthmeasuring signals averaged by the pulse number count value of thepreceding measurement, and measurement before that. When Xm(n-1) andXm(n-2) differ, the operation proceeds to RETURN; when they are equal,the process advances to step 403. Instep 403 the operation calculates asurge index S indicative of torque variation, as a function f1 of Nem,Nec and Xm(n-1). Further, in step 404 a dispersion V(c) of the surgeindex S is calculated. This V(c) corresponds to the torque.

In step 405 it is determined whether the dispersion V(c) is larger thana predetermined torque variation limit value VL. When V(c)≦VL, it isdetermined that there is no abrupt torque variation, and processingRETURNS to the start. When V(c)>VL, it is deemed that there is an abrupttorque variation, and in step 406 a difference ΔV between V(c) and VL iscalculated. Further, in step 407 the operation calculates a correctedair fuel ratio ΔKMR as a function f2 of ΔV and Nec, rewrites the data ofthe target air fuel ratio KMR to KMR+ΔKMR in step 408, and proceeds toRETURN.

FIG. 5 shows the process performed by blocks 306 to 308 in FIG. 3.First, in step 501 the operation reads output signals from an oxygensensor A/F, an air flow sensor Qa, the above-mentioned KMR and Nec.Next, in step 502, it is determined whether KMR is 14.7 (theoretical airfuel ratio). For this purpose, it is necessary to determine with highaccuracy the actual air fuel ratio in the lean burn region by the oxygensensor. Therefore, the operation corrects the target air fuel ratio datawhen the air fuel ratio is 14.7, which can be detected by the oxygensensor. When the determination is Yes in step 502, it is determined tostep 503 whether the target air fuel ratio KMR is equal to the actualair fuel ratio A/F. If so, the operation proceeds to step 504 and holdsa correction constant k1 at the previous calculation. When they are notequal, the operation proceeds to step 505 and calculates the correctionconstat k1 from a function f3 of KMR and A/F, to correct it. In step 506the data table of the target air fuel ratio KMR is searched. Next, instep 507 the operation calculates a fuel amount Ti by multiplying afunction f4 of ΔKMR, KMR, Nec and Qa by k1, and outputs it in step 508.When the determination is No in step 502 (that is, the air fuel ratio isnot 14.7), the operation proceeds to step 504 because the air fuel ratiocannot be corrected.

FIG. 6 is a flow chart which shows the operation of blocks 304 and 305in FIG. 3. First, the air fuel ratio KMR is read in step 601. Then, instep 602 it is determined whether the target air fuel ratio KMR is equalto or less than a NOx emission limit air fuel ratio KMR0, which ispreviously set as, for example, 22. When the determination is No, theoperation proceeds to RETURN. When it is Yes, in step 603 the data tableof the target air fuel ratio KMR is rewritten to 14.7, to prevent anincrease in the emission amount of NOx.

FIG. 7 is an operational characteristic which shows the relationshipbetween the air fuel ratio and the amount of NOx emission in the controlaccording to the first embodiment of the present invention. For example,suppose that the air fuel ratio of a lean burn engine is set to 25 whenit is new. Thereafter, the lean burn limit air fuel ratio is graduallyreduced to less than 25 by aging. As shown in FIG. 7, the farther theair fuel ratio falls below 25, the more the NOx emissions increase.Therefore, the air fuel ratio reaches 22, it is step wisely changed tothe theoretical air fuel ratio of 14.7, to prevent the amount of NOxfrom the increasing. In this manner, fuel cost reduction and exhaust gaspurification can be compatible with each other.

FIGS. 8 through 10 show a second embodiment of the present invention inwhich control of air intake is added to the control of the firstembodiment shown in FIG. 2. Portions the same as those in FIG. 2 areattached with the same notations. In the method which controls only thefuel intake as shown in the first embodiment, torque variation due tothe change of the air fuel ratio cannot be completely eliminated;therefore, control of air intake is indispensable. First, a targettorque calculating unit 801 calculates a target torque required by adriver. The target torque and the actual torque detected by the torquedetecting units 206 are compared in a comparing unit 802 and a deviationdetected therebetween is used to calculate a target air amount in atarget air amount calculating unit 803. A throttle opening degreecalculating unit 804 calculates a target throttle opening degree andoutputs control data to the throttle controlling device 18, which maybe, for example, an electronic control throttle valve in which thethrottle valve is opened and closed by driving a motor, an idling speedcontrolling device, a supercharger and a variable valve timingcontrolling device etc.

FIG. 9 is a flow chart which shows the operation of the control shown inFIG. 8. First, the operation reads an accelerator opening degree ∝, thepulse number count signal Nec, speed Nt of the output shaft of thetorque converter and the target air fuel ratio KMR. In step 902 a targetengine torque Tetar required by a driver is calculated as a function f5of α and Nec. Next, processing proceeds to step 903 and calculates anactual engine torque Tereal from the characteristic of the torqueconverter, by multiplying square of Nec by a pump capacity coefficient cthat is a function of Nt and Nec. Further, in step 904 a correctedengine torque ΔTe is calculated using the results in steps 902 and 903,and the target engine torque Tetar is corrected in step 905. In step 906the process searches data tables of Tetar and Nec for every target airfuel ratio KMR and calculates a target throttle opening degree. Finally,the operation outputs the throttle opening degree in step 907.

Although the operation has used data tables to calculate the throttleopening degree, the calculation may of course be performed by forming amodel constructed by equations in place of the data tables. Further, fordetection of the actual engine torque, it is also possible to use anactual torque sensor attached to the drive shaft, a combustion pressuresensor directly detecting the pressure in cylinders of internalcombustion engine, and rotation sensors detecting a difference inrotation (torsion) attached to the front and the end of the drive shaft.

FIGS. 10 through 13 show a third embodiment of the present invention.FIG. 10 is a conceptual block diagram showing maps of a basic control ofa lean burn internal combustion engine, in which control or ignitiontiming is added to the above embodiments. In this system the targetengine torque of an internal combustion engine is used as a reference.Map 1001, is a family of characteristics of engine torque and the enginespeed for various throttle openings, at an air fuel ratio of 14.7. Whenthese characteristics are used as the target, the operatingcharacteristic of a conventional internal combustion engine (not a leanburn type) can be satisfied. Here, the accelerator opening degree (inplace of the throttle opening degree) and the engine speed are enteredas inputs. (In the example, an engine speed of about 2200 rpm and anaccelerator opening of 10% are shown.) To satisfy the torque required bya driver the actual engine torque is conformed to the target enginetorque which is outputted.

The fuel amount, the air amount and the ignition timing are determinedbased on the target engine torque and the engine speed. First, withregard to the fuel amount, there may be a case where misfire is causeddepending on the operating region, (for example, in lean mixture) andthere may be a case where the mixture cannot be made lean consideringthe output at high rotation and high load of the engine. Accordingly,the regions of the air fuel ratio are classified as shown in a map 1002.(In the example of FIG. 10, here, the air fuel ratio of 23 is selected.)

Next, in a map 1003 the air fuel ratio (23), the target engine torqueand the engine speed are used as inputs to select a target throttleopening degree, which is outputted. Finally, in a map 1004 the targetignition timing is selected and outputted, based on the target enginetorque and the engine speed. A value of MBT (Minimum Advance of the BestTorque) is set to the ignition timing.

FIG. 11 is a block diagram of a torque control arrangement according tothe invention which includes control of ignition. In this embodiment, asignal of an air fuel ratio data change finish determining unit 1101(for determining whether the change of the air fuel ratio data has beencompleted) and a signal of the torque detecting unit 206 (for detectingthe state of the torque of the output shaft) are inputted to an MBTdetermining unit 1102. The MBT determining unit 1102 detects the stateof torque for controlling the ignition timing (as explained hereinbelow)by which the MBT is determined. An ignition timing correcting unit 1103corrects the ignition timing in accordance with the state of torquedetermined by the MBT determining unit 1102, and a target ignitiontiming data changing unit 1104 changes the value stored in a targetignition timing data storing unit 1105 in accordance with the result ofcorrection.

A comparison interrupt signal generating unit 1106 sends a comparisoninterrupt signal to a comparing unit 1107, so that the throttle openingdegree is not changed, during calculation of the ignition timing MBT. Anignition timing calculating unit 1108 then calculates the ignitiontiming using data from the ignition timing correcting unit 1103 and thetarget ignition timing data storage unit 1105 and outputs it to anignition device 1109 such as the ignition plug 6 shown in FIG. 1. Whenthe MBT determining unit 1102 determines that the ignition timingcorresponds to the value for the MBT, comparison interruption signalgenerating unit 1106 outputs a signal to the comparing unit 1107 tocommence comparison, and allows throttle control. The throttle controlin correspondence with the torque change due to the ignition timingcontrol is similar to the content described in FIG. 8.

FIGS. 12 and 13 are flow charts which show the operation of the controlarrangement shown in FIG. 11. In FIG. 12, first, in step 1201, theoperation reads the accelerator opening degree α, the pulse number count(engine speed) signal Nec, the torque converter output shaft speed Nt,the target air fuel ratio KMR, an air fuel ratio change flag FlgA and anair fuel ratio change state flag FlgB. In step 1202 the actual enginetorque Tereal is calculated using the characteristic of the torqueconverter, in a manner similar to the description of FIG. 9. Next, instep 1203 it is determined whether FlgA is 1.

If it is 1, the change of the air fuel ratio data has been finished, andthe operation proceeds to step 1204, carrying out the MBT control. (WhenFlgA is other than 1, the operation proceeds to RETURN.) In step 1204,the a comparison discontinuation start flag FlgC is set to the value 1,stopping correction by the throttle control (or intake air amountcontrol). Next, processing proceeds to step 1205, where it is determinedfrom FlgB whether the air fuel ratio has moved in the direction of arich air fuel ratio or a lean air fuel ratio by FlgB. In case of therich air fuel ratio (FlgB=1) the process advances to step 1206 and incase of the lean air fuel ratio (FlgB=0) proceeds to step 1207. Ineither case, the MBT is detected, for example, by means of a feedbackprocess comprising steps 1208-1209. That is, in step 1206 (or 1207) theengine timing is incremented by subtracting or adding 1 degree to thecrank angle. In step 1208 the actual engine torque Tereal at this timeis input with the actual engine torque Tereal(n-1) of the precedingtime, and in step 1209, the change of the engine torque caused bychanging the ignition timing is determined and fed back. In step 1209,when Tereal is less than or equal to Tereal(n-1), processing advances tostep 1210, rewrites the region of the target ignition timing adv to avalue of adv+Δadv, writes 0 to the comparison discontinuation start flagFlgC in step 1211, and proceeds to RETURN. If Tereal is greater thanTereal (n-1) in step 1209, processing returns to step 1205 and steps1205-1209 are repeated in an iterative process.

FIG. 13 is a flow chart of the ignition timing control by interruption.In step 1301 the operation reads the corrected ignition timing Δadv, theair amount Qa and the pulse number count (engine speed) signal Nec. Instep 1302, the operation searches the data table of the ignition timingadv and calculates the target ignition timing ADV based on theabove-mentioned adv and Δadv in step 1303. Further, the operationoutputs the target ignition timing ADV in step 1304.

FIGS. 14 and 15 show a forth embodiment of the present invention. FIG.14 is a block diagram which shows an embodiment of a control accordingto the invention which prevents shock caused by the change of the airfuel ratio. First, the operation inputs the engine speed and theaccelerator opening degree to a processing unit 1401, which calculatesthe target engine torque required by a driver. Next, in block 1402, atarget fuel injection pulse width is calculated in conformity with thetarget engine torque. At the same time the operation also uses a reverseintake pipe model (block 1403) to calculate the air amount (throttleopening degree, opening degree of a shunt valve) in conformity with thetarget engine torque (that is, in conformity with the target fuelinjection width), and outputs it. In this manner, in changing the airfuel ratio, the target engine torque is also set while the acceleratoropening stays constant and a fuel injection width is retained, so thatthe air fuel ratio can be changed without torque variation.

To carry out the fuel amount control with high accuracy, it is necessaryto calculate the actual fuel injection width in a processing unit 1404by feeding back the signals from an air intake amount sensor and thespeed sensor to correct the target fuel injection width. Further, innormal (steady state) operation, the process feeds back signals of theoxygen sensor etc. and corrects the air fuel ratio map in a processingunit 1405, thereby correcting the target fuel injection width. This fuelretaining control is suitable in changing the air fuel ratio in both thetransient state and steady state.

FIG. 15 illustrates time charts for explaining the control shown in FIG.14. The relative location of the throttle valve and the shunt valvesaffects the relationship between the opening of these valves and theengine output torque. Referring to FIG. 1, it is necessary to considerthe inertia of the intake air flow in the intake pipe between thethrottle control device 18 incorporating the throttle valve and theswirl shunt valves 19. Therefore, there is a time lag between a changein the opening of the throttle valve and the opening of the swirl shuntvalves 19, as shown in FIG. 15. The openings of these valves arecalculated processing unit 1403 using the reverse intake pipe in modelin FIG. 14. When the air fuel ratio is changed while the target enginetorque stays constant, the air amount is changed by the control shown inFIG. 15 while maintaining the fuel amount constant. In this manner, theair fuel ratio can be changed without varying the torque.

As shown in the above embodiments, the present invention provides theoutput torque control method and apparatus for a lean burn internalcombustion engine without adverse effect on fuel cost, poisonous exhaustgas emissions and operational performance. Lean burn combustion controlcan be achieved in conformity with the request of a driver inconsideration of aging of component parts of a lean burn internalcombustion engine and component parts of the control device.

FIGS. 16 through 27 show a fifth embodiment of the present invention.FIG. 16 is a block diagram of a fifth embodiment of the invention, whichreduces variation of the output torque of an engine by controlling theair fuel ratio in a switching operation, wherein the air fuel ratio incombustion at a theoretical air fuel ratio is switched to that of leanburn. In FIG. 16, a target air fuel ratio calculating unit 1608calculates the target air fuel ratio based on the accelerator depressionangle detected by an accelerator pedal angle detector 1601, the intakeair amount detected by an intake air flow detector 1602 and the enginespeed detected by an engine speed detector 1603. An air fuel ratioswitch time fuel injection amount calculating unit 1604 calculates thefuel injection amount for switching the air fuel ratio, based on theaccelerator depression angle, the engine speed and the target air fuelratio calculated by the target air fuel ratio calculating unit 1608. Asteady state fuel injection amount calculating unit 1605 calculates thefuel injection amount in steady state operation, based on the enginespeed, the intake air amount and the target air fuel ratio. An air fuelratio switch time throttle opening calculating unit 1606 calculates thethrottle opening for switching the air fuel ratio, based on the targetair fuel ratio from the calculator 1608, the intake air amount detectedfrom detector 1602, the engine speed and the accelerator depressionangle. A steady state throttle opening calculator 1607 calculates thethrottle opening for steady state operation based on the engine speed,the intake air amount, the accelerator depression angle and the targetair fuel ratio from the calculator 1608.

An air fuel ratio switch detecting unit 1611 detects switching of theair fuel ratio, based on the target air fuel ratio from the calculator1608. A fuel injection value selecting unit 1609 switches from the fuelinjection value calculated by the steady state fuel injection valuecalculating unit 1605 to the value calculated by the air fuel ratioswitch fuel injection value calculating unit 1604 during switching ofthe air fuel ratio (detected by the air fuel ratio switch detecting unit1611), and switches it back to the value calculated by the steady statefuel injection value calculating unit 1605 when the switching of the airfuel ratio is completed.

A throttle opening value selecting unit 1610 switches from the throttleopening value calculated by the steady state throttle openingcalculating unit 1607 to the value calculated by the air fuel ratioswitch time throttle opening calculating unit 1606 during switching ofthe air fuel ratio (detected by the air fuel ratio switch time detectingunit 1611), and switches it back to the value calculated by the steadystate throttle opening calculating unit 1607 when switching of the airfuel ratio is completed. A fuel injection pulse generating means 1612generates pulses based on the fuel injection value selected by the fuelinjection value selecting unit 1609. A throttle driving means 1613drives the throttle based on the calculated value of the throttleopening selected by the throttle opening value selecting unit 1610.Further, in this case, the control of the air amount may be performednot only by the throttle valve but also by valves for idling speedcontrol (hereinafter, ISC) a supercharger, a turbo for controlling amotor etc.

FIG. 17 shows the relationship between the air fuel ratio A/F and thefuel amount, and FIG. 18 shows a relationship between the air fuel ratioA/F and the emission amount of NOx, both when the output of an enginestays the same. Generally, in a lean burn internal combustion engine,the air fuel ratio is switched by decreasing or increasing the fuelinjection amount without changing the opening of the throttle valve(that is, without changing the intake amount). Therefore, in changingthe air fuel ratio the output torque of an engine changes, whichadversely affects the handling of the vehicle as perceived by a driveror passengers. In this embodiment, to counter this effect, the air fuelratio is switched by opening and closing the throttle valve to controlthe air amount, while maintaining the fuel injection amount constant.However, when the air fuel ratio is made lean while generating the sameoutput, the necessary fuel amount is decreased as shown in FIG. 17.Therefore, it is necessary to finely adjust the fuel injection amount tomaintain the output torque constant during switching of the air fuelratio. The NOx generating amount has a peak value in ratio of 14.7 to 21through 24 as shown in FIG. 18. Therefore, when the switching of the airfuel ratio is performed slowly, the NOx generating amount is increased,which adversely affects exhaust gas purification. Accordingly, theswitching of the air fuel ratio must be performed rapidly to decreasethe NOx generating amount.

FIG. 19 is a time chart which shows the change of the output torque ofan engine due to switching the air fuel ratio, when the value of thefuel injection amount Ti is maintained constant. In a transient state,during which the target air fuel ratio is changed from 14.7 to 24, acontrol signal is outputted by the air fuel ratio switch detecting unit1611 in FIG. 16, and the method of calculating the fuel injection valueTi and the throttle opening TVO are changed. The throttle opening TVOand the intake amount Qa change in a manner similar to that of thetarget air fuel ratio. However, the fuel injection amount Ti ismaintained constant. As a result, the output torque is slightlyincreased due to the lean air fuel ratio. In this manner, rapid changeof the output torque due to switching of the air fuel ratio isrestrained by maintaining the fuel injection amount Ti constant andchanging the intake amount Qa. Thus, the switching of the air fuel ratiocan be finished in a short period of time and the generation of NOx canbe reduced. However, when the fuel injection amount Ti is maintainedconstant, a slight variation of the torque occurs. This small variationcan be restrained by decreasing the fuel injection amount Ti inaccordance with the change of the target air fuel ratio and the increasein the generated torque per fuel amount.

FIG. 20 is time chart which shows the change of the output torque dueswitching the air fuel ratio, when the increase of the output torque isrestrained by slightly changing the fuel injection amount. During atransient state in which the target air fuel ratio is changed from 14.7to 24, a control signal is outputted by the air fuel ration switchdetecting unit 1611 in FIG. 16, whereby methods of calculating the fuelinjection value Ti and the throttle opening TVO are switched. Thethrottle opening TVO and the intake amount Qa change in a manner similarto that of the target air fuel ratio. The fuel injection value Ti isreduced slightly in accordance with an increase in the target air fuelratio. Accordingly, the small increase in the output torque isrestrained and torque shock or adverse handling effects can beprevented, even when the air fuel ratio is changed rapidly.

FIG. 21 is a flow chart which shows calculation performed by the airfuel ratio switch time fuel injection value calculating unit 1604 shownin FIG. 16. First, in step 2101, the process detects the acceleratordepression angle and the engine speed Ne in step 2102. In step 2103 atarget basic fuel injection pulse width Tp is determined from a map,based on the engine speed Ne and the accelerator depression angle θth.Next, in step 2104 a map is used to determine a relative fuelconsumption rate η' with respect to the target air fuel ratio by settingthe fuel consumption rate at the theoretical air fuel ratio of 14.7as 1. Finally, an actual fuel injection pulse width Tp' is calculated bythe following equation (1) in step 2105:

    Tp'=Tp×η'                                        (1)

FIG. 22 is a flow chart which shows the calculation performed by thesteady state fuel injection value calculating unit 1605 shown in FIG.16. First, the operation detects the engine speed Ne in step 2201 andthe intake air amount Qa in step 2202. Next, the basic fuel injectionpulse width Tp is calculated by the following equation (2) in step 2203:

    Tp=Qa/Ne×K A/F×K                               (2)

where K A/F is a constant determined by air fuel ratio and K is aconstant which is independent of the air fuel ratio. Next, in step 2204the actual fuel injection pulse width Tp' is calculated according toequation (3) below, by multiplying the basic fuel injection pulse widthTp by the relative fuel consumption rate determined by the target airfuel ratio.

    Tp'=×Tp                                              (3)

FIG. 23 shows the calculation performed by the air fuel ratio switchthrottle opening calculating unit 1606 in FIG. 16. First, the operationdetects the engine speed Ne in step 2301 and calculates the targetintake air amount Qa' in step 2303 by the equation (4) below, bymultiplying a total fuel injection amount Qf by the target air fuelratio A/F.

    Qa'=Qf×(A/F)                                         (4)

Finally, in step 2303 the operation calculates the target throttleopening degree by mapping based on the engine speed Ne and the targetintake air amount Qa'.

FIG. 24 is a flow chart which shows the calculation performed by thesteady state time throttle opening calculating unit 1607. First, theaccelerator depression angle θth and the engine speed Ne in steps 2401and 2402. In step 2403, the operation calculates the target basic intakeamount Qa by mapping based on the accelerator depression angle θth andthe engine speed Ne. Next, in step 2404, a target intake amount Qa' iscalculated by multiplying the target basic intake amount Qa by a ratioof the target air fuel ratio to the theoretical air fuel ratio.

    Qa'=Qa ×                                             (5)

Further, the operation calculates a target throttle opening degree TVO'by mapping from the target intake amount Qa' and the engine speed Ne.

FIG. 25 is a flow chart which shows the calculation performed by the airfuel ratio switch time detecting unit 1611 shown in FIG. 16. In step2501, the operation compares a current target air fuel ratio with apreceding target air fuel ratio, and determines whether the target airfuel ratio has been switched. If so, the operation proceeds to step2502, and if not, it proceeds to step 2503. In step 2502 the operationoutputs Yes, and outputs No in step 2503. Further, in step 2504, theoperation is finished when the current target air fuel ratio is equal tothe preceding target air fuel ratio.

FIG. 26 shows the calculation performed by the fuel injection valueselecting unit 1609 in FIG. 16. In step 2601, the operation checkswhether the air fuel ratio is to be switched. If so, processing advancesto step 2602, and to step 2603 if not. In step 2602, the operationoutputs the calculated value of the air fuel ratio switch time fuelinjection value calculating unit 1604. In step 2603, the operationoutputs the calculated value of the steady state fuel injection amountcalculating unit 1605.

FIG. 27 shows the calculation performed by the throttle opening valueselecting unit 1610 in FIG. 16. In step 2701, the operation checkswhether the air fuel ratio is to be switched. If so, the operationproceeds to step 2702, and proceeds to step 2703 if not. In step 2702,the operation outputs the calculated value of the air fuel ratio switchtime throttle opening calculating unit 1606, while in step 2703, theoperation outputs the calculated value of the steady state throttleopening calculating unit 1607.

As stated above, according to the present invention, stepwise change oftorque or shock in switching the air fuel ratio is restrained to thegreatest extent possible, the air fuel ratio can be switched rapidly andthe emission amount of NOx can be reduced.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample, and is not to be taken by way of limitation. The spirit andscope of the present invention are to be limited only by the terms ofthe appended claims.

What is claimed is:
 1. An output torque control apparatus for aninternal combustion engine, comprising:an accelerator opening degreesensor detecting an accelerator opening degree; an engine speed sensordetecting an engine speed; an engine torque detector detecting a presentengine torque; a fuel supply actuator controlling a fuel amount suppliedto said engine; an air supply actuator controlling an air amount suckedto said engine; and a data processor unit for setting a detected presentengine torque as a target engine torque, for calculating a controlamount for said actuators in accordance with said target engine torqueand a detected engine speed, and for outputting a fuel amount controlsignal to said fuel supply actuator for controlling said fuel amount,and an air amount control signal, which is calculated in accordance withsaid fuel amount control signal, and supplied to said air supplyactuator for controlling said air amount.
 2. An output torque controlapparatus for an internal combustion engine, comprising:an acceleratoropening degree sensor detecting an accelerator opening degree; an enginespeed sensor detecting an engine speed; a fuel supply actuatorcontrolling a fuel amount supplied to said engine; an air supplyactuator controlling an air amount sucked to said engine; and a dataprocessor unit for calculating a target engine torque in accordance witha detected accelerator opening degree and a detected engine speed, forcalculating a fuel control amount in accordance with said target enginetorque, for calculating an air control amount in accordance with saidfuel control amount and for outputting said fuel control amount to saidfuel supply actuator and said air control amount to said air supplyactuator.